Most flooring materials are currently prepared from polyvinyl chloride (PVC). PVC usually contains significant amounts of phthalate plasticizers (more than about 30% by weight based on PVC) to produce sufficient flexibility and impact strength for flooring material applications. The flooring materials are typically prepared by thermo-mechanically mixing PVC, phthalate plasticizer, fillers like calcium carbonate and additives followed by a calendering process to prepare the desired flooring sheets. Examples of various processes are described in U.S. Pat. Nos. 4,826,912, 4,804,429, 4,225,374, 3,951,714, 4,605,584, 5,670,237, 5,700,865, and 5,945,472, the contents of which are hereby incorporated by reference. There is an interest in developing alternative renewable materials for use in flooring.
Research has been undertaken in some areas of plastics engineering to use biodegradable materials as reagents in the synthesis of plastic materials. Castor oil is an example of such a material. Castor oil is a natural product produced internationally in commodity quantities. Of all the commercial oils generated from agricultural oil seed products, castor oil exhibits some special characteristics that have made it a dominant commercial vegetable oil. Extracted from the seeds or “beans” of the plant Ricinus Communis, which grows in many tropical and warm temperate regions throughout the world, castor oil is one of the few naturally occurring triglycerides that exist in the natural state as a single, pure compound. Castor oil primarily includes the triglyceride of the hydroxyl acid, ricinoleic acid. In fact, ricinoleic acid is typically around 90% of the total triglyceride fatty acids in castor oil and is a commercial material that has multiple functional groups in its molecular structure. The pendant hydroxyl (—OH), the unsaturated, carbon-carbon double bond (—C═C—), and the carboxyl group (—COOH) in ricinoleic acid all provide reactive sites for preparing many useful industrial products.
Sebacic acid and castor oil have been used to form estolide prepolymers (L. H. Sperling and J. A. Manson, JAOCS, 60(11):1887–1891 (1983)). Interpenetrating network polymers have also been generated using castor oil and isocyanates to generate polyurethane-based polymer structures, as described, for example, in U.S. Pat. No. 4,254,002, GB Patent No. 1 057 044, GB Patent No. 1 023 393, AU Patent No. 687982, EP Patent No. 0 361 170, AU Patent No. 1504595, and JP Patent No. 8053530, the contents of which are hereby incorporated by reference. Additional information regarding castor oil urethanes can be found in Sperling et al., J. Polym. Mater. 1,54 (1984), Patel and Suthar, Polym. Eng. Sci., 28, 901 (1988), and Nayak et al., J. Appl. Polym. Sci., 47, 1089 (1993). Examples of interpenetrating networks formed from castor oil include those in which the hydroxy groups in the castor oil are crosslinked with diisocyanate compounds and the double bonds are crosslinked with styrene monomers to form castor oil-based polyurethane interpenetrating polymer networks (IPNs).
Epoxidized soybean oil (ESO), an epoxidized derivative of a naturally occurring vegetable oil, is commonly used as a secondary plasticizer for polyvinyl chloride (PVC) materials. The use of ESO is known to impart flexibility, strength and ultraviolet stability to PVC resin formulations. However, it has not been used to date in combination with castor oil or ricinoleic acid to prepare polymeric materials. Further, IPNs based on ricinoleic acid have not yet been prepared, and those castor oil-based polyurethane IPNs are prepared from extremely toxic and hazardous isocyanate moieties. Extreme care must be used in manufacturing processes that use isocyanates, as exposure to isocyanates is known to be fatal.
In light of the growing environmental awareness, increasing societal concern and new environmental rules and regulations, it would be advantageous to have ecologically friendly materials for flooring applications that provide the flooring with desirable physical and mechanical properties. The present invention provides such materials.